cmux/Sources/WindowDragHandleView.swift

import AppKit
import Bonsplit
import SwiftUI

private func windowDragHandleFormatPoint(_ point: NSPoint) -> String {
    String(format: "(%.1f,%.1f)", point.x, point.y)
}

private func windowDragHandleEventTypeDescription(_ eventType: NSEvent.EventType?) -> String {
    eventType.map { String(describing: $0) } ?? "nil"
}

private enum WindowDragHandleBreadcrumbLimiter {
    private static let lock = NSLock()
    private static var lastEmissionByKey: [String: CFAbsoluteTime] = [:]

    static func shouldEmit(key: String, minInterval: CFTimeInterval) -> Bool {
        lock.lock()
        defer { lock.unlock() }

        let now = CFAbsoluteTimeGetCurrent()
        if let previous = lastEmissionByKey[key], (now - previous) < minInterval {
            return false
        }
        lastEmissionByKey[key] = now
        if lastEmissionByKey.count > 128 {
            let staleThreshold = now - max(minInterval * 4, 60)
            lastEmissionByKey = lastEmissionByKey.filter { _, timestamp in
                timestamp >= staleThreshold
            }
        }
        return true
    }
}

private func windowDragHandleEmitBreadcrumb(
    _ message: String,
    window: NSWindow?,
    eventType: NSEvent.EventType?,
    point: NSPoint,
    minInterval: CFTimeInterval = 10,
    extraData: [String: Any] = [:]
) {
    let windowNumber = window?.windowNumber ?? -1
    let key = "\(message):\(windowNumber)"
    guard WindowDragHandleBreadcrumbLimiter.shouldEmit(key: key, minInterval: minInterval) else {
        return
    }

    var data: [String: Any] = [
        "event_type": windowDragHandleEventTypeDescription(eventType),
        "point": windowDragHandleFormatPoint(point),
        "window_number": windowNumber,
        "window_present": window != nil
    ]
    for (name, value) in extraData {
        data[name] = value
    }
    sentryBreadcrumb(message, category: "titlebar.drag", data: data)
}

private func windowDragHandleShouldResolveActiveHitCapture(
    for eventType: NSEvent.EventType?,
    eventWindow: NSWindow?,
    dragHandleWindow: NSWindow?
) -> Bool {
    // We only need active hit resolution for titlebar mouse-down handling.
    // During launch, NSApp.currentEvent can transiently point at a stale
    // leftMouseDown from outside this window (for example Finder/Dock
    // activation). Treat those as passive events so we never walk SwiftUI/
    // AppKit hierarchy while initial layout is mutating it.
    guard eventType == .leftMouseDown else {
        return false
    }
    guard let dragHandleWindow else {
        // Test-only views may not be attached to a window.
        return true
    }
    guard let eventWindow else {
        return false
    }
    return eventWindow === dragHandleWindow
}

/// Runs the same action macOS titlebars use for double-click:
/// zoom by default, or minimize when the user preference is set.
@discardableResult
func performStandardTitlebarDoubleClick(window: NSWindow?) -> Bool {
    guard let window else { return false }

    let globalDefaults = UserDefaults.standard.persistentDomain(forName: UserDefaults.globalDomain) ?? [:]
    if let action = (globalDefaults["AppleActionOnDoubleClick"] as? String)?
        .trimmingCharacters(in: .whitespacesAndNewlines)
        .lowercased() {
        switch action {
        case "minimize":
            window.miniaturize(nil)
            return true
        case "none":
            return false
        case "maximize", "zoom":
            window.zoom(nil)
            return true
        default:
            break
        }
    }

    if let miniaturizeOnDoubleClick = globalDefaults["AppleMiniaturizeOnDoubleClick"] as? Bool,
       miniaturizeOnDoubleClick {
        window.miniaturize(nil)
        return true
    }

    window.zoom(nil)
    return true
}

private enum WindowDragHandleAssociatedObjectKeys {
    private static let suppressionDepthToken = NSObject()

    static let suppressionDepth = UnsafeRawPointer(Unmanaged.passUnretained(suppressionDepthToken).toOpaque())
}

func beginWindowDragSuppression(window: NSWindow?) -> Int? {
    guard let window else { return nil }
    let current = windowDragSuppressionDepth(window: window)
    let next = current + 1
    objc_setAssociatedObject(
        window,
        WindowDragHandleAssociatedObjectKeys.suppressionDepth,
        NSNumber(value: next),
        .OBJC_ASSOCIATION_RETAIN_NONATOMIC
    )
    return next
}

@discardableResult
func endWindowDragSuppression(window: NSWindow?) -> Int {
    guard let window else { return 0 }
    let current = windowDragSuppressionDepth(window: window)
    let next = max(0, current - 1)
    if next == 0 {
        objc_setAssociatedObject(
            window,
            WindowDragHandleAssociatedObjectKeys.suppressionDepth,
            nil,
            .OBJC_ASSOCIATION_RETAIN_NONATOMIC
        )
    } else {
        objc_setAssociatedObject(
            window,
            WindowDragHandleAssociatedObjectKeys.suppressionDepth,
            NSNumber(value: next),
            .OBJC_ASSOCIATION_RETAIN_NONATOMIC
        )
    }
    return next
}

func windowDragSuppressionDepth(window: NSWindow?) -> Int {
    guard let window,
          let value = objc_getAssociatedObject(window, WindowDragHandleAssociatedObjectKeys.suppressionDepth) as? NSNumber else {
        return 0
    }
    return value.intValue
}

func isWindowDragSuppressed(window: NSWindow?) -> Bool {
    windowDragSuppressionDepth(window: window) > 0
}

@discardableResult
func clearWindowDragSuppression(window: NSWindow?) -> Int {
    guard let window else { return 0 }
    var depth = windowDragSuppressionDepth(window: window)
    while depth > 0 {
        depth = endWindowDragSuppression(window: window)
    }
    return depth
}

/// Temporarily enables window movability for explicit drag-handle drags, then
/// restores the previous movability state after `body` finishes.
@discardableResult
func withTemporaryWindowMovableEnabled(window: NSWindow?, _ body: () -> Void) -> Bool? {
    guard let window else {
        body()
        return nil
    }

    let previousMovableState = window.isMovable
    if !previousMovableState {
        window.isMovable = true
    }
    defer {
        if window.isMovable != previousMovableState {
            window.isMovable = previousMovableState
        }
    }

    body()
    return previousMovableState
}

/// SwiftUI/AppKit hosting wrappers can appear as the top hit even for empty
/// titlebar space. Treat those as pass-through so explicit sibling checks decide.
func windowDragHandleShouldTreatTopHitAsPassiveHost(_ view: NSView) -> Bool {
    let className = String(describing: type(of: view))
    if className.contains("HostContainerView")
        || className.contains("AppKitWindowHostingView")
        || className.contains("NSHostingView") {
        return true
    }
    if let window = view.window, view === window.contentView {
        return true
    }
    return false
}

/// Returns whether the titlebar drag handle should capture a hit at `point`.
/// We only claim the hit when no sibling view already handles it, so interactive
/// controls layered in the titlebar (e.g. proxy folder icon) keep their gestures.
func windowDragHandleShouldCaptureHit(
    _ point: NSPoint,
    in dragHandleView: NSView,
    eventType: NSEvent.EventType? = NSApp.currentEvent?.type,
    eventWindow: NSWindow? = NSApp.currentEvent?.window
) -> Bool {
    let dragHandleWindow = dragHandleView.window

    // Suppression recovery runs first so stale depth is cleared even for
    // passive events — the associated-object reads/writes here are pure ObjC
    // runtime calls and cannot trigger Swift exclusive-access violations.
    if isWindowDragSuppressed(window: dragHandleWindow) {
        // Recover from stale suppression if a prior interaction missed cleanup.
        // We only keep suppression active while the left mouse button is down.
        if (NSEvent.pressedMouseButtons & 0x1) == 0 {
            let clearedDepth = clearWindowDragSuppression(window: dragHandleWindow)
            windowDragHandleEmitBreadcrumb(
                "titlebar.dragHandle.suppression.recovered",
                window: dragHandleWindow,
                eventType: eventType,
                point: point,
                minInterval: 20,
                extraData: [
                    "cleared_depth": clearedDepth
                ]
            )
            #if DEBUG
            dlog(
                "titlebar.dragHandle.hitTest suppressionRecovered clearedDepth=\(clearedDepth) point=\(windowDragHandleFormatPoint(point))"
            )
            #endif
        } else {
        #if DEBUG
            let depth = windowDragSuppressionDepth(window: dragHandleWindow)
            dlog(
                "titlebar.dragHandle.hitTest capture=false reason=suppressed depth=\(depth) point=\(windowDragHandleFormatPoint(point))"
            )
        #endif
            return false
        }
    }

    // Bail out before the view-hierarchy walk so we never re-enter SwiftUI
    // views during a layout pass — which causes exclusive-access crashes (#490).
    if !windowDragHandleShouldResolveActiveHitCapture(
        for: eventType,
        eventWindow: eventWindow,
        dragHandleWindow: dragHandleWindow
    ) {
        #if DEBUG
        let eventTypeDescription = eventType.map { String(describing: $0) } ?? "nil"
        let eventWindowNumber = eventWindow?.windowNumber ?? -1
        let dragWindowNumber = dragHandleWindow?.windowNumber ?? -1
        dlog(
            "titlebar.dragHandle.hitTest capture=false reason=passiveEvent eventType=\(eventTypeDescription) eventWindow=\(eventWindowNumber) dragWindow=\(dragWindowNumber) point=\(windowDragHandleFormatPoint(point))"
        )
        #endif
        return false
    }

    guard dragHandleView.bounds.contains(point) else {
        #if DEBUG
        dlog("titlebar.dragHandle.hitTest capture=false reason=outside point=\(windowDragHandleFormatPoint(point))")
        #endif
        return false
    }

    guard let superview = dragHandleView.superview else {
        #if DEBUG
        dlog("titlebar.dragHandle.hitTest capture=true reason=noSuperview point=\(windowDragHandleFormatPoint(point))")
        #endif
        return true
    }

    let siblingSnapshot = Array(superview.subviews.reversed())

    #if DEBUG
    let siblingCount = siblingSnapshot.count
    #endif

    for sibling in siblingSnapshot {
        guard sibling !== dragHandleView else { continue }
        guard !sibling.isHidden, sibling.alphaValue > 0 else { continue }

        let pointInSibling = dragHandleView.convert(point, to: sibling)
        if let hitView = sibling.hitTest(pointInSibling) {
            let passiveHostHit = windowDragHandleShouldTreatTopHitAsPassiveHost(hitView)
            if passiveHostHit {
                #if DEBUG
                dlog(
                    "titlebar.dragHandle.hitTest capture=defer point=\(windowDragHandleFormatPoint(point)) sibling=\(type(of: sibling)) hit=\(type(of: hitView)) passiveHost=true"
                )
                #endif
                continue
            }
            #if DEBUG
            dlog(
                "titlebar.dragHandle.hitTest capture=false point=\(windowDragHandleFormatPoint(point)) siblingCount=\(siblingCount) sibling=\(type(of: sibling)) hit=\(type(of: hitView)) passiveHost=false"
            )
            #endif
            windowDragHandleEmitBreadcrumb(
                "titlebar.dragHandle.hitTest.blockedBySiblingHit",
                window: dragHandleWindow,
                eventType: eventType,
                point: point,
                minInterval: 8,
                extraData: [
                    "sibling_type": String(describing: type(of: sibling)),
                    "hit_type": String(describing: type(of: hitView))
                ]
            )
            return false
        }
    }

    #if DEBUG
    dlog("titlebar.dragHandle.hitTest capture=true point=\(windowDragHandleFormatPoint(point)) siblingCount=\(siblingCount)")
    #endif
    return true
}

/// A transparent view that enables dragging the window when clicking in empty titlebar space.
/// This lets us keep `window.isMovableByWindowBackground = false` so drags in the app content
/// (e.g. sidebar tab reordering) don't move the whole window.
struct WindowDragHandleView: NSViewRepresentable {
    func makeNSView(context: Context) -> NSView {
        DraggableView()
    }

    func updateNSView(_ nsView: NSView, context: Context) {
        // No-op
    }

    private final class DraggableView: NSView {
        override var mouseDownCanMoveWindow: Bool { false }

        override func hitTest(_ point: NSPoint) -> NSView? {
            let currentEvent = NSApp.currentEvent
            // Fast bail-out: only claim hits for left-mouse-down events.
            // For mouseMoved / mouseEntered / etc., return nil immediately
            // to avoid re-entering SwiftUI view state during layout passes,
            // which causes exclusive-access crashes.
            guard currentEvent?.type == .leftMouseDown else {
                return nil
            }
            let shouldCapture = windowDragHandleShouldCaptureHit(
                point,
                in: self,
                eventType: currentEvent?.type,
                eventWindow: currentEvent?.window
            )
            #if DEBUG
            dlog(
                "titlebar.dragHandle.hitTestResult capture=\(shouldCapture) point=\(windowDragHandleFormatPoint(point)) window=\(window != nil)"
            )
            #endif
            return shouldCapture ? self : nil
        }

        override func mouseDown(with event: NSEvent) {
            #if DEBUG
            let point = convert(event.locationInWindow, from: nil)
            let depth = windowDragSuppressionDepth(window: window)
            dlog(
                "titlebar.dragHandle.mouseDown point=\(windowDragHandleFormatPoint(point)) clickCount=\(event.clickCount) depth=\(depth)"
            )
            #endif

            if event.clickCount >= 2 {
                let handled = performStandardTitlebarDoubleClick(window: window)
                #if DEBUG
                dlog("titlebar.dragHandle.mouseDownDoubleClick handled=\(handled ? 1 : 0)")
                #endif
                if handled {
                    return
                }
            }

            guard !isWindowDragSuppressed(window: window) else {
                #if DEBUG
                dlog("titlebar.dragHandle.mouseDownIgnored reason=suppressed")
                #endif
                return
            }

            if let window {
                let previousMovableState = withTemporaryWindowMovableEnabled(window: window) {
                    window.performDrag(with: event)
                }
                #if DEBUG
                let restored = previousMovableState.map { String($0) } ?? "nil"
                dlog("titlebar.dragHandle.mouseDownComplete restoredMovable=\(restored) nowMovable=\(window.isMovable)")
                #endif
            } else {
                super.mouseDown(with: event)
            }
        }
    }
}